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authorGrygorii Strashko <grygorii.strashko@ti.com>2013-03-16 11:46:47 +0530
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-03-25 13:18:13 -0700
commitf02503b2ff73d3b09ca27335304611a206d2b54a (patch)
treeb378994b306e55cc2fd2fab20449637e5e1250f9 /drivers/memory/emif.c
parent36caf3e525b24556f649aecd097cad73bde6f035 (diff)
downloadlinux-f02503b2ff73d3b09ca27335304611a206d2b54a.tar.bz2
memory: emif: errata i743: Prohibit usage of Power-Down mode
ERRATA DESCRIPTION : The EMIF supports power-down state for low power. The EMIF automatically puts the SDRAM into power-down after the memory is not accessed for a defined number of cycles and the EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field is set to 0x4. As the EMIF supports automatic output impedance calibration, a ZQ calibration long command is issued every time it exits active power-down and precharge power-down modes. The EMIF waits and blocks any other command during this calibration. The EMIF does not allow selective disabling of ZQ calibration upon exit of power-down mode. Due to very short periods of power-down cycles, ZQ calibration overhead creates bandwidth issues and increases overall system power consumption. On the other hand, issuing ZQ calibration long commands when exiting self-refresh is still required. WORKAROUND : Because there is no power consumption benefit of the power-down due to the calibration and there is a performance risk, the guideline is to not allow power-down state and, therefore, to not have set the EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field to 0x4. This is applicable only for EMIF4D IP used in OMAP4 Soc's. Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com> Signed-off-by: Vitaly Chernooky <vitaly.chernooky@ti.com> Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@ti.com> Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com> Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/memory/emif.c')
-rw-r--r--drivers/memory/emif.c35
1 files changed, 35 insertions, 0 deletions
diff --git a/drivers/memory/emif.c b/drivers/memory/emif.c
index 9335339ebfdf..bd223c7c3e72 100644
--- a/drivers/memory/emif.c
+++ b/drivers/memory/emif.c
@@ -257,6 +257,41 @@ static void set_lpmode(struct emif_data *emif, u8 lpmode)
u32 temp;
void __iomem *base = emif->base;
+ /*
+ * Workaround for errata i743 - LPDDR2 Power-Down State is Not
+ * Efficient
+ *
+ * i743 DESCRIPTION:
+ * The EMIF supports power-down state for low power. The EMIF
+ * automatically puts the SDRAM into power-down after the memory is
+ * not accessed for a defined number of cycles and the
+ * EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field is set to 0x4.
+ * As the EMIF supports automatic output impedance calibration, a ZQ
+ * calibration long command is issued every time it exits active
+ * power-down and precharge power-down modes. The EMIF waits and
+ * blocks any other command during this calibration.
+ * The EMIF does not allow selective disabling of ZQ calibration upon
+ * exit of power-down mode. Due to very short periods of power-down
+ * cycles, ZQ calibration overhead creates bandwidth issues and
+ * increases overall system power consumption. On the other hand,
+ * issuing ZQ calibration long commands when exiting self-refresh is
+ * still required.
+ *
+ * WORKAROUND
+ * Because there is no power consumption benefit of the power-down due
+ * to the calibration and there is a performance risk, the guideline
+ * is to not allow power-down state and, therefore, to not have set
+ * the EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field to 0x4.
+ */
+ if ((emif->plat_data->ip_rev == EMIF_4D) &&
+ (EMIF_LP_MODE_PWR_DN == lpmode)) {
+ WARN_ONCE(1,
+ "REG_LP_MODE = LP_MODE_PWR_DN(4) is prohibited by"
+ "erratum i743 switch to LP_MODE_SELF_REFRESH(2)\n");
+ /* rollback LP_MODE to Self-refresh mode */
+ lpmode = EMIF_LP_MODE_SELF_REFRESH;
+ }
+
temp = readl(base + EMIF_POWER_MANAGEMENT_CONTROL);
temp &= ~LP_MODE_MASK;
temp |= (lpmode << LP_MODE_SHIFT);